Application of Solution Cathode Glow Discharge-Atomic Emission Spectrometry for the Rapid Determination of Calcium in Milk
HAO Jun1, WANG Yu2, LIU Cong2, WU Zan2, SHAO Peng2, ZU Wen-chuan2*
1. School of Environmental Science & Engineering，Tianjin University，Tianjin 300072，China
2. Institute of Analysis and Testing，Beijing Academy of Science and Technology（Beijing Center for Physical & Chemical Analysis）, Beijing 100089, China
Abstract：The content of calcium is closely associated with the quality of milk. The traditional analytic methods based on tedious wet digestion or dry ashing preparation techniques are low efficiency. Meanwhile, the milk samples for determination are too much as milk is an important and common food origin for calcium nutrient income. Therefore, it’s in urgent demand for the establishment of the rapid and field analytic method of calcium in milk. Recently, significant attention has been drawn to solution cathode glow discharge-atomic emission spectrometry (SCGD-AES) due to the absence of vacuum conditions as well as the addition of airflow of the fuel and carrier gas, etc. Thus, a portable SCGD-AES instrument was developed with an inside CCD detector, through which practicability for calcium determination in milk was inspected based on direct dilution sampling. Furthermore, the rapid and convenient method was established to rapidly determine calcium in milk using a home-made solution cathode glow discharger coupled with a portable optical fiber spectrometer based on direct dilution sampling. The conditions and parameters influencing the analytical sensitivity of potassium were optimized comprehensively, including the emission wavelength, the acidity of the cathode solution, etc. The results showed that acidity was a key parameter influencing the analytical sensitivity, and when 1%（V/V）HNO3 was used as the medium，the best analytical performances could be acquired. Therefore，1% （V/V） HNO3 was chosen as the dilution reagent. Furthermore, the selection of the dilution times of the real milk samples was investigated. The results showed that when the milk samples were diluted to 100 times or above, no significant matrix interference was observed and the accuracy could be assured. Under the optimized conditions, when the milk sample was diluted 100 times, the limit of determination for calcium in milk was 35 mg·L-1, which was just suitable for the direct determination, and the relative standard deviations based on 6 duplicate tests of the same milk sample were below 5%. The spiked recoveries were within the range of 89.0%~109.7%. The results showed that the method was simple and reliable and could satisfy the demands of rapid detection of calcium in milk for laboratory and field tests.
